1. Field of the Invention
This invention relates to a paper feeder constructed so as to feed perforated paper, the perforations in which are fitted over the feed pins of a feed belt, by moving this feed belt by a driving sprocket, and more particularly to an integral frame type paper feeder having a main frame formed integrally so as to improve the rigidity thereof, whereby the paper feed accuracy is heightened.
2. Description of the Prior Art
A main frame of a paper feeder houses therein a driving assembly consisting of a feed belt, and a driving sprocket used to drive this feed belt.
The main frame of a conventional paper feeder is formed by combining a plurality of parts by a connecting means as shown in, for example, FIG. 21, which illustrates two frame members 51, 52 constituting side plates and combined with each other by a connecting bolt 53. Therefore, this main frame has the following various kinds of inconveniences.
(1) The main frame is formed by combining a plurality of parts, and each part necessarily has assembly tolerance. Accordingly, the accuracy and rigidity of the main frame decrease due to the part assembling work.
(2) When the two frame members 51, 52 are combined with each other in a dislocated state as shown in FIGS. 22 and 23, a difference occurs between paper feed clearances C, C' defined by the upper surfaces of the frame members 51, 52 and the opposed surface of a cover member 54, so that the paper feed accuracy lowers.
(3) The clearance of a slide portion of a feed belt 55 is determined on the basis of the main frame assembling accuracy. Accordingly, when this clearance is small, the feed belt 55 is clamped by the frame members 51, 52 to cause the rotary torque, which is necessary for moving the feed belt 55, of a driving sprocket 56 to increase. When this clearance is large, the feed belt 55 becomes loose while in motion, to cause the paper feed accuracy to lower.
(4) The side plates consisting of the frame members 51, 52 which constitute the main frame are provided therein with bores 57 for supporting the driving sprocket 56, and bores 58 for receiving a support shaft. If the axes of the bores 57 for supporting the driving sprockets 56 become out of alignment with each other due to the decrease in the main frame assembling accuracy, the rotational resistance of the driving sprocket 56 becomes high, so that the torque required to rotate the same sprocket increases. Similarly, if the axes of the bores 58 for receiving the support shaft therein become out of alignment with each other, the paper clamping effect of the paper feeder decreases to an unsatisfactory level, and troubles occur when the paper feeder is moved laterally along the support shaft. Moreover, the paper feeder inclines when the paper is clamped.
(5) Since the main frame is formed by combining a plurality of parts with one another, it necessarily incurs frame assembling cost, so that the cost of manufacturing the main frame increases as compared with that of an integrally formed main frame. In addition, the number of parts of the main frame increases, and the part manufacturing cost and the control expenses for the parts also increase.
Therefore, it is an object of the present invention to provide a paper feeder in which a main frame is formed integrally to improve both the rigidity of the main frame and the assembling accuracy of the paper feeder, whereby the paper feed accuracy of the paper feeder is improved to eliminate the above-mentioned inconveniences of the main frame of a part-assembly structure completely.